If you are using SAFESTRAP: if on your safe side, all you need to do is wipe data and cache several times before flashing another ROM. No need for an SBF.
If using BOOTSTRAP: to answer your question, yes, Mav4.0 was updated to the .906 as the base. So, if you used Bootstrap to flash over stock, then yes, you'll need Ovelayer's .906 SBF. Then you'll need to take the OTA again.